Re: RMAN - Some basic Qs.

In case of hot backup scn at then time of starting backup is frozen in datafile header , and is refreshed at the time of end backup .what happens in RMAN ?

-ak

• Original Message ----- To: "Multiple recipients of list ORACLE-L" <ORACLE-L_at_fatcity.com> Sent: Tuesday, April 01, 2003 12:43 PM

> All,
>
> The primary reason why RMAN does not generate
> excessive redo is because because it does not put the
> tablespace in "hot backup mode". Thus any blocks
> belonging to a given tablespace that are modified
> before the END BACKUP command is processed, do not
> require block-level before and after images. Hence the
> reduction in redo generation.
>
> So how does RMAN backup without "hot backups"?
>
> RMAN is aware of the format of an Oracle datafile, and
> reads datafiles for the backup in DB_BLOCK_SIZE
> chunks. This is not the case with most OS utilities
> (tar, cpio, cp, dd etc.), which read files in 512-byte
> OS blocksize chunks.
>
> As a result, the issue of a fractured block (for which
> block-level before/after images are taken) on the
> destination where the backup is done, does not come
> into play in RMAN.
>
> Hope that helps,
>
> Gaja
>
> --- "Goulet, Dick" <DGoulet_at_vicr.com> wrote:
> > 1: RMAN does not generate excessive redo because it
> > does not use the 'alter tablespace ... begin backup'
> > command. It instead coordinates with dbwr, somehow,
> > to be sure it is getting a consistent view of the
> > tablespace.
> >
> > 2: The concept of an incremental backup is that you
> > only backup the database blocks that have changed
> > since the last incremental of the same or higher
> > level. Somehow the date that the block changed is
> > being managed, probably in the header somewhere.
> >
> > 3: If your reading a block for backup purposes, it's
> > pretty easy to checksum it and compare with what's
> > in the header just like the Oracle kernel does.
> >
> > 4: I've tried before with OmniBack and it's fairly
> > simple. You only have to relink Oracle including a
> > MML library file. The package you want to integrate
> > with should have instructions.
> >
> > Dick Goulet
> >
> > -----Original Message-----
> > Sent: Tuesday, April 01, 2003 10:19 AM
> > To: Multiple recipients of list ORACLE-L
> >
> >
> >
> > Qs.1 Why is NO excessive Redo Generated wsing RMAN
> > Backups unlike HOT Backups
> > when taking backup of an OPEN Database which is
> > undergoing User Transactions ?
> > (Or am i mistaken ?)
> >
> > Qs.2 How does RMAN manage Incremental Database
> > Backups ? What is the Concept behing it ?
> >
> > Qs.3 How does RMAN Check for Block Corruption while
> > taking backup ?
> >
> > Qs.4 Is it easy to integrate 3rd part tools like
> > Legato etc with RMAN for enabling taking
> > of backups onto backup devices OR does it need an
> > extensive setup ?
> >
> >
> > --
> > Please see the official ORACLE-L FAQ:
> > http://www.orafaq.net
> > --
> > Author: VIVEK_SHARMA
> > INET: VIVEK_SHARMA_at_infosys.com
> >
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> Please see the official ORACLE-L FAQ: http://www.orafaq.net
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> Author: Gaja Krishna Vaidyanatha
> INET: oraperfman_at_yahoo.com
>
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-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.net
-- 
Author: AK
  INET: oramagic_at_hotmail.com

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